1. Field of the Invention
The present invention relates to a circuit arrangement for positioning printing mechanisms in printers, and is more particularly concerned with determining the position of a printing mechanism which is driven by a d.c. motor, where the position is determined by the number which is displayed on a counter and which is determined by counting the pulses of an optical scanner in a positive direction and in a negative direction.
2. Description of the Prior Art
In end-of-text printing devices, such as teleprinters and typewriters, frequently the printing mechanism is moved relative to a stationary platen. Generally, the printing mechanism is driven by a separate motor or via a toothed belt or the like.
It is known to determine the position of the printing mechanism relative to the platen or to the data carrier by optically scanning the slots in a scanner disc which is attached to the motor shaft of the driving d.c. motor. In order to detect a clearly-defined position, normally two incremental scanners are required which, when a shaft rotates, emit two pulse signals, electrically displaced in phase by 90.degree.. The position of the printing mechanism is determined in that the pulses emitted from the optical scanner are added and, in fact, with a positive sign in one movement of direction of the printing mechanism and with a negative sign in the other direction. The positive or negative sign is obtained from the phase position of the two pulse signals. The scanners employed in this arrangement both need to be electrically and/or mechanically adjusted, which requires a relatively high expense.